Teletypewriter synchronizing arrangement



May1.,1945. w. B. MARTI A2,375,125

TELETYPEWRITER SYNCHRONIZING ARRANGEMEN'II Filed Dec. 22, 1943 ase u Relerllse De 1.5 Seconds Stop Genelvztol' IVENTOR M11/jin f ATTORNEY Patented May 1,- 1945 UNITED! srarss ra'ren'rl ortica TELETYPEWRITER SYNCHRONIZIN G ARRANGEMENT Wade E. Martin, Westwood, N. J., assigner' to American Telephone and Telegraph Company, a corporation of New York Application December 22, 1943, Serial No. 515,251

24 Claims.

This invention relates to teletypewriter systems, and particularly to arrangements to locally generate the start-stop impulses accompanying a character determining code so that such impulses wil be automatically supplied to the receiver even when, Vbecause of momentary circuit failure, they are not received from the transmitting station.

In operating teletype receivers over transmission media such as radio waves or other kinds of channels subject to numerous random failures of short duration, two types of errors occur. (1) The failure may cause an error in one or more of the ve units of the Baudot code which determines the character to be printed, thus causing a wrong character to be recorded; or (2) it may result in receiving the wrong kind of pulse instead of the stop pulse or the start pulse.

The rst of these conditions is not as serious as the second. If one or more'of the ve character determining pulses should be distorted or reversed it merely causes some other character to be printed instead of the one intended. The message will usually be intelligible in spite of the error. If, however, an improper stop pulse is received the receiving distributor does not come to a momentary stop at the end of the code combination, and hence gets ahead of the transmitter. Similarly, if an improper start signal is received, the receiving distributor is not released until a message pulse transition occurs ofthe same nature as the normal start pulse. The receiver therefore falls behind the transmitter.

After an early or late start is received the receiving mechanism may lose synchronism with the transmitter and a number of character errors will be received before synchronism is regained. This number may vary from one to'seven. In regaining the proper phase relation the receiver may operate one time more or less than the transmittel'. In receiving normal English teXt this will result in a number of miscellaneous letters being received, after which synchronism will be regained and the text will again be intelligible. If, however, the message is in cipher the addition or subtraction of one or more characters in the received message, as described above, will cause the deciphering code to lose synchronism with the enciphering code and the message will be unintelligible thereafter.

It is therefore the object of the present invention to overcome errors caused by circuit troubles which result in false start and stop signals. This is accomplished by associating with the receiver a local generator of start and stop 4pulses which will introduce such pulses into the receiver regardless of whether or not they are properly reK ceived fromthe transmitter. y n

Preferably the apparatus is so arranged thatv at the start of a message, after the circuit hasv been idle for a time, the start and stop impulses, will be received directly from the line as usual.v In the meantime the local stop-start pulse generator is set into action, after which the receiver is disconnected from the line while the stop pulse andthe beginning of the start pulse should be rec eived, but is again connected during the period f when the end of the start pulse and the ve character determining pulses are normally re ceived, and the local stop-start generator is con-` nected to the receiver during the time the stop, and start pulses are normally sent from the transmitter.

This principle ofoperation is subject to theA disadvantage that the locally generatedv stopstart pulses may gradually get out of phase with the corresponding pulses sent from the sending station. Accordingly the present invention` prof. vides means kto overcome this difculty. The apparatus is so designed that when the stop and4 start pulses incoming from the line are diverted from the receiver, the corresponding pulses are supplied locally, the stop-start impulses comingv in from the line are applied to the local genera'- tor. The generator is so arranged that when. these pulses are received Without distortion, thev stop to start transition automatically synichronizes the local generators.

Further details and features of the invention will be clear upon reading the following detailed description in connection with the acompanying drawing. Figure l of the drawingillustrates circuitl arrangement embodying the invention, said arrangement employing, a vacuum tube timing circuit to control the local generation of stop and start pulses, with a similar timing circuit to control the connection of the line to the receiver during the reception of character determining pulses. Fig. 2 shows a similar circuit arrange` ment employing a regenerative repeater as the timing device to perform the last named. func.- tion.

vGeneral description of apparatus of Fig. 1

For purposes of illustration the pulse generating apparatus herein disclosed is described 'as operating 368 times per minute, i. e'., it completes each full cycle in 163 milliseconds. Thisis approximately the time ordinarily required for a start-stop system to send a start pulse, ve char-. acter determining pulses and a stop pulse. The

ing or open circuit pulse is received the armature v will be moved by the influence ofthe biasillg.` winding b to the spacing contact. The armature of relay RR is normally connected to the Vlocal teletype receiver symbolically; represented; at TTY over a contact 3 of a time-outrelay TOR whose purpose will appear later.

A vacuum tube timing circuit VT1 is provided to control the local generation of stop and start pulsestq synchronize theoperation of the distributor (not shown) of the receiver TTY;-v 'This timing circuit includes a vacuum tube VT1, a capacityCi, andra variable resistance R1, these elements being so related that when negative voltage is applied directlyto the capacity and to the `grid rof the `tube the .tube will instantly become` nonrconductive, but when said voltage is withdrawn the condenser `vvill be gradually discharged and`a.proper voltage built up to render the tube VTil fully conductive only after the lapse of a predeterminedtime. This time may be 31 millisecondscor .the period of anormal stop `pulse.

VAn adjustable potentiometer P1 is .associated with` .the timing circuit TG1.4 The dropv through a part of thel potentiometer Vmay be either positive or negative depending upon Whether onnot a positive start impulse or a negativestop impulse isrelayed. to it by the` receiving relay RR.` dropl is utilized to decrease or increase the time normally required to render the-tube VT; fully This enablesthe timing circuit `TG1 conductive. to, be brought. intosynchronization with` the stop. start impulses transmitted from the sending-statiorrwhen` properly received. asV will. appear more fully later- A similar, timingcircuit TCL is provided to control the `transmission of ypulses from the receivingrelay RR to the receiver TTY during the reception of character. determining pulses. This timingcircuitincludesa .vacuum tube VTz, a1. condenser Cz, and a variableresistance R2. These elements areso related and adjusted that when a negative potential is applied directly to the ca-y when tube VT1 is conductive, the circuit being from positive battery via the operating winding of relay LTR and the biasing winding b of relay SGRz to the plate of tube VTi. In the case of relay SGR2 its biasing winding b is energized by the plate current oi the tube VTi when said tube is fully conductive, Whilefits operating Winding o is energized partly by negative current supplied through a resistance R4 and partly by current supplied through. resistance R3 from the armature of, receiving relay RR.

The functions of the stop generator relay SGRi are to supply over contact 4 of said relay the stop pulse to the teletypwriter, and to control over contact .5 the operation of the timing circuit TCi which, byop'erating relay SGR'z to open its contact 4,. generatesa. start pulse to be applied to the receiver TTY locally. The functions of the start generator relay SGRz are to terminate the stop pulse` locally supplied to thereceiver, thus causing a start pulse tc be. supplied Ato the receiver, and tocontrol theoperation of .the timing circuit TCz. When the operating winding o of -the relay SGRi is de-energized, as it is during the period the timing Vcircuit TCz is completing its cycle and before vacuum .tube VTz becomes conductive, during which period, thelstart Vpulse and character` determining pulses are normally trans-` mitted, the armature of the relay .,SGRi is on its contact Sand disables thevacuum. tube VT2.

When said armature of relay SGRi is shifted to its contact 4 a stop pulse is locallyy transmitted tothe receiver TTY and timingcircuit TG1 begins its cycle, causing vacuum tube VT1 to become conductive. After approximately 31 milliseconds (in the. design herein. disclosed) vacuum l tube VTL Ibecomes fully rconductive so that the .relay SGRashifts its Varmaturefrom contact 4to contact 5 ,to terminate the stop pulse` and produce a no current or start condition in the circuit vof the receiver TTY. Also the vacuum tube VTz of the timing circuit TG2 is :disabled during the period necessary for timing circuit TG2 to complete another cycle-and for vacuumtube VT2 -to build up anv operating current for the operating Winding o of relay-SGRl This current attains fulloperatn ing value attheend of aperiod of approximately i determining. pulse has been received. Then- 13.2 milliseconds, i. e., after the last character relayy SGR1 shifts its armature from its contact 5 to contact 4 and the cycle of operation begins anew.

Aspreviously stated the operating winding o of line transfer relay LTR is energized by the circuit .TG2 serves to. control, the connection 'ofi Y the receiver TTY to the armature of the receiving relay RR during the reception'of the character determining pulses in a manner to be described later.`

Three. additional polar relays` are provided, a stop'generator relay SGR1, a start generator .relay vSGRz, and a. line transfer relay L'I'R.` The operatingwindings 0.0i -relays SGR1 and` LTR are operated fby the plate current of vacuum tube VTz-vvhen` the ,latter is. fully conductive.v The operating winding o of relay LTR is also operated plate circuit of vacuum tube VTz. When the armature of4 relayLTR is on its contact 5 the ar' mature of receiving relay RR is connected to the receiver. TTY. Said armature Will been its contact 5 after the condenser C5 has become charged, and vvvhile the timing circuit TG2 is completing the execution of its cycle. Operating space current' does not flow inv operating Winding o of relay LTR under: these conditions. During this period'the marking and spa-cingpulses of the Baudot code determining the characters are sent to. the receiver. When the; armature of line transfer relayLTR is on-contact 4i the connection from the armatureofreceiving relay RR to receiver TTY is transferred to the potentiometer P1, Consequently ywhen a normal stop-start transition comes inr from the loop L it controls the operation. ofthe timing circuits TCrand' TG2 to. synchronize the local generation of a stopsta'rt transitionv with that Yreceived from the loopf generated stop-start pulses to the receiver.

functions-to break the normal connection from the armature of the receiving relay RR to the receiver TTY. It also substitutes alternative con-l nections for receiving character determining pulses from the loop L, and for supplying locally To energize the relay TOR a bridged rectifier unit BR is provided. The bridged rectier unit BR includes four rectiers arranged .in the arms of a Wheatstone bridge, one junction of which is connected through resistance Rs to the armature of the receiving relay RR, and the opposite junction of which is connected to ground through a condenser C4. The winding of slow release relay TOR is bridged across the other two terminals of the bridge.

' The four rectiers are so poled that a pulse of vcurrent of one polarity from the armature of receiving relay RR passes through the upper right rectifier, through the winding of relay TOR from right to left, and through the lower left rectifier to charge the condenser C4. Pulses of opposite polarity will pass from ground through the condenser C4, through the lower right rectier, through the 'Winding of relay TOR from right to left, and through the upper left rectier and resistance Rs to the armature of relay RR. It should be noted that pulses of either polarity passs through the relay TOR in the samedirection.

It is evident that as the armature of the receiving relay RR is shifted from marking to spacing and vice versa, the condenser C4 will be alternately charged positive and negative. As the condenser is thus -charged spurts of direct current pass through the winding of the relay TOR in the same direction. These spurts do not persist duri ing the entire period thatcurrent continues in` the same direction in the loop L, but occur only at the beginning of each pulse and flow only as long as is required to charge the condenser C4 in a given direction.

The effect of the current in the winding of the relay TOR depends upon the constants of the circuit and the number of operations per second of the armature of relay RR. Single random transitions such as result from momentary circuit failures will not cause reiay TOR to operate. When, however, transitions occur repeatedly at relatively sho-rt intervals, as is the case when normal teletypewriter signaling takes-place, the relay TOR will operate after the reception of one or more characters, depending on the number of transitions in the characters.

The magnetism in the relay TOR will continue building up for an appreciable time as successive transitions occur. Consequently there is a wide range between the release time atthe start of transmission and that after the relay has neared saturation. Due to these characteristics and `those above mentioned the circuitsl established by the relay TOR for controlling the stop-start pulse generator can readily distinguish between actual signal transmission and circuit interference.

When the receiving relay RR remains steadily in either marking or spacing condition, due to the conclusion of signal transmission or due to line failure, the condenser C4 will reach a steady state of charge. Spurts of current will no longer pass through the winding of relay TOR and hence it will release. The time required for it to release its armature is determined by. theV design and adjustrnent of the relay and the degree .of satura-- tion it has reached.

In actual practice the releasing time has been made.l.5 seconds following a full signal interval. With this releasing time it has been found that on the average the relay TOR was held up long enough so that if a line failure occurs after two characters have been received, one additional local vstop-start transition was automatically generated thereafter. A failure after a third character resulted in two start-stopv transitions. A failure after a fourth character resulted in four transitions, and after a fifth character, in six transitions, A failure occurring after receiving seven or more characters resulted in automatically generating eight to ten transitions without the line returning to normal. Thus it will be seen `that the locally generated start-stop pulses will keep the receiver operating in approximate synchronization with thetransmitting station for a period as long as is necessary to transmit eight to ten characters even though the line fails.

Normal or idle condition of circuit of Fig. 1

Assume that the line (not shown) has been idle and the loop L has been in closed'condition over a period long enough for all apparatus to have been restored to normal condition. Under these circumstances the armature of the receiving relay RR will be resting on its contact 4. Relay TOR is de-energized and hence the armature of relay RR is connected directly to the receiving teletypewriter TTY over contact 3 of relay TOR. Another circuit extends from` the armature of relay RR over contact li of relay LTR, contact L of relay TOR, through resistance R3 and operating windn ing o of relay SGRz to ground, As the armature of relay RR is on its marking contact negative battery is thus applied to the winding o of relay SGRz, holding the armature of said relay operated toits contact ll in opposition to the action of the space current flo-wing through the biasing winding of relay SGRz from the plate of vacuum tube VT1.

The armature of relay SGRz is on its contact 4 so that the lead to the timing circuit TCz is open. Hence condenser Cz has fully discharged through resistance R2 any previous negative charge built l up in it, and the grid of vacuum tube VTz is positive. Full operating space current therefore flows from the output of said tube through the operating winding o of relays SGRi and LTR. The armatures of said relays rest yon their number 4 contacts. Relay LTR thus establishes the circuit previously traced through the winding o of relay SGRz. With the armature of relay SGRi on its contact ll, negative battery is disconnected from timing circuit TC1, and the condenser Ci has discharged to positive battery through resistance R1, causing the grid of tube VTi to become positive and allowing space current to flow through vacuum tube VTi to bias winding b` of relay SGR2.

Reception of first character by circuit of Fig. 1

' (relay TOR not operated) Assume4 now that a start pulse is received in loop L so that an open circuit condition is produced in the loop. The biasing winding of relay RR shifts its armature to its spacing contact, thus transmitting a start pulse over contact 3 of relayl TOR to receiver TTY. When the armature of relay RR is on its spacing contact, positive battery is applied over this circuit. Since positive battery is also connected to the circuit beyond resmaller than resistance R4 this positive current prevails over the negative current throughresistance RA, and winding o of relay-SGRz is activated by av reduced current flowing in the Opposite direction from that previously existing. Winding o of relay SGRz now aids biasing winding b so that the armature of said relay is shifted from contact 4 to contact 5.

With the armature 'of relay SGRz on its contact 5 negative potential is applied over contact 4 oi relaySGRi, and contact 5 of relay SGRz to condenser C2 andthe grid of tube VTz of the timing circuit TCi. Condenser Cz' receives a full negative-charge and current is immediately suppressed in theplatecircuit of` vacuum tube VT2. This suppresses current in the operating winding o of relay SGR1 but current is maintained in the operating `winding of relay LTR because vacuum tube VTi is stillconductive. `Relay SGRi shifts its. armature to its contact 5.

As the armature of relay SGRr leaves its contact 4,\the `negative battery previously applied to condenser C2 is removed and the condenser begins to slowly dischargeto positive battery through the rheostat R2. The rheostat is adjusted so that the condenser will be completely discharged and the vacuum; tube VT: will become fully conductive in' about 132 milliseconds. This period is equivalent vto ithe time required `to transmit a start pulse. and uve character determining pulses to the' receiver TTY.

Returning,` however, to the beginning of the 132.*millisecond interval, when the armatureof relay;- SGrRi` shifted to its Contact 5 due to the disabling-of the tube VTz, it connected negative battery to the condenser C1 and grid of vacuum tube VTi of the timing circuit TCi. The coni denser isthus chargedto negative potential and current is at once'suppressed in the plate circuit of ltube VTi. However, current Acontinues to flow inrthe windings o of relay LTR and b of relay SGR2 for approximately 22 milliseconds by the action of condenser Ce.y After said condenser discharges, current'ceases to flow in the winding b ofl relay SGR2 and the operating winding of the relay LTR, thus operating relay LTR to its number-5contact. This disconnects the positive current from winding o of relay SGRzso that the negative current owing in said winding through l resistance R4 shifts the armature of relay SGR/2 back again to its contact 4. Thus it will be seen that although relay SGR2 operates to its contact 5 when a start pulse is received, it reverts back toits contact 4 after approximately 22 milliseconds -due to the operation of relay LTR to its number 5 contact, and thus prepares a path for the stop pulse to be transmitted to the teletype- Writer.

` It will benoted thatWhen the armatureof relay LTR movesY to its contact 5 analternative path is established from the armature of relay RR over Said contact 5to the receiver TTY. This path, which is independent of the direct path over contact 3 of relay TOR., is established approximately 22milliseconds after the start pulse is received, and ismaintained for llomilliseconds, the period requiredfor vacuum tubeVTz to become fully conductive. Thus-:this alternative path is maintained for a time *.suicientl'y longto` permitthe liveV character pulses to be transmitted to the receiver over this path. The establishment of thiscircuit is not important at this time, however, but becomes of importance later whenthe relay TOR is operated, as will appear in due course.

Assuming that at the end of 132 milliseconds the relay TOR has not yet received a suicient number of spurts of current to activate it, the following operations now take place:

Normally a stop pulse will be received about 132 milliseconds after the start pulse is received. Quite independently of the reception of the stop pulse the timing circuit TG2 has at this time just completed its cycle and the vacuum tube VTZ has become fully conductive. The armatures of relays SGR; and LTR therefore move to their con'- tacts 4.

As the armature' of relay LTR leaves its contact 5 the alternative pathirom the armature of relay RR to receiver TTY over contact 5 of relay LTR is broken. When the armature of relay LTR strikes its Contact 4 a circuit is established from the armature of the receiving relay RR, the armature and contact 4 of relay LTR, and the armature and number 2 Contact of relay TOR to the resistance Rz and the operating winding of relay SGRz, placing the operation of relay SGRz again under the control of the combined action of the receiving relay RR, and vacuum tube VT1.

As the armature of relay SGR1 leaves its contact 5 the negative potential is removed from condenser C1 andthe grid of vacuum tube VT1. The timing circuit Ci-Rl starts discharging, and at the end of about 31 milliseconds the vacuum tube VT1 becomes fully conductive so that full biasing current will llow through the winding b of relay SGRz and the winding o of relay LTR.y The armature of relay SGRz will be shifted to its contact 5 at this time, if, as should be the case, the received stop impulse ends and a start succeeds it. When the armature of relay SGRz thus shifts to its contact 5 the cycle of timing circuits TCz and TCi are started anew.

Reception of characters by circuit of Fig.1 after relay TOR operates We have considered the operation of the circuit of Fig. 1 under the conditions existing While the relay TOR. remains de-energized. Let us now suppose that some time during the reception of the character determining pulses identifying the second character of the message, a suiiicient number of transitions from negative to positive and vice versa have occurred to energize the relay TOR. It will be remembered that while character determining pulses are being received, the armatures of relays SGR1 and LTR rest upon their number 5 contacts, and the armature of relay SGRz rests upon its contact 4. The timing circuit TG1 is therefore disabled by a negative potential applied to th'e grid of vacuum tube VTi, and the timing circuit TCais going through its 132millisecond cycle at the endl of which a current will flow in the'plate circuit of vacuum tube VTz.

When the relay TOR operates it shifts its left hand armature from contact 'l to contact 2. Theicpeningof 'contact I breaks the circuit (now also open at contact 4 of relay LTR) which was previously traced from the armature of receiv` directly responsive to start pulses incoming from the loop L, but Will now be either underI the control of negative current through the resistance R4 or of positive current'from the plate circuit of vacuum tube VT1, and will so continue as long as relay TOR remains operated.

Relay TOR at its contact 2 prepares a circuit (now open at contact 4 of relay LTR) from the armature of receiving relay RR, over contact 4 of relay LTR when closed, over contact 2 of relay TOR, through resistance R5 and potentiometer P1 to ground. This circuit operates, as will more fully appear later, to synchronize'the operating time of the circuit TG1 forthe generation of start pulses, so that the stop-start transitions produced locally by the timing circuits Will coincide with the stop-start transitions in the loop L, if proper stop-start pulses are received in said loop.

At its contact 3 relay TOR opens the direct connection for pulse transmission from the armature of receiving relay RR to the receiving instrument TTY.- So long as relay TOR remains energized character determining impulses must be transmitted over the alternative path previousmaintained in reasonable synchronization with i the sending station even though stop-start pulses occasionally fail to be receivedin the loop L.

'With the circuits of the receiving station modied as,above described, let us consider what takes place when the last of the ve character determining pulses has been sent to the receiver TTY and the stop pulse is being received. About the time the stop pulse should normally arrive, the'timing circuit TG2 will have completed its cycle and full operating current will have been built up in the plate circuit of the tube VTz. Relay SGRi now shifts its armature'from contact 5 to contact Ll, and relay LTR similarly shifts its armature.

During the time the armature of relay SGR1 rested on its contact 5, condenser C1 of timing circuit TC1 received a definite negative charge. Upon breaking contact 5 of relay SGR1' condenser C1 starts discharging through resistance R1. The

manner in which the timing circuit TC1 now functions will be more fully described later, in

connection with the description of the synchroi nizing operation determinedA by potentiometer P1 under the control of stop-start pulses received from loop L.

As relay SGR1 closes its contact 4, a circuit is established from negative battery over contact 4 of relay SGR1, over contact 4 of relay SGRQ, through resistance Re and over contact 4 of relay TOR; to receiver TTY. Thus a.stop pulse is sent to receiver TTY independently of the stop pulse (if any) received in loop L. This pulse continues while the timing circuit TC1 goes through its cycle to build up full operating current in the plate circuit of vacuum tube VT1 for the energization of the biasing Winding b of relay SGRz. In the meantime this pulse is maintained by the operating Winding o of said relay which is energized by negative current through resistance R4.

Relay LTR operates to shift its armature from contact 5 tol contact 4. When the armature of relay LTR leaves Contact 5 the path from the receiving relay armature to the teletypewritery is opened and the teletypewriter is noW under the control of relays SGR1 and SGRz as explained before. When the armature of relay LTR strikes contact 4 a circuit is completed which will serve to synchronize the local generation of stop-start pulses as will be described later. Relay LTR armature Will remain on its contact 4, under the combined action of currents in its operating winding o from vacuum tubes VT2 and VT1, and the charging condenser C5 from the start of the optimum stop pulse, until the end of the optimum start pulse, except that the start pulse may be lengthened or shortened as will be explained later.

The synchronization 0f the timing circuits TCi and. T02 with respect to received stop-start pulses is effected by increasing or decreasing the time cycle of circuit TC1. When the relay LTR operates to its contact 4 it opens its contact 5 and thereby opens the connection from the armature of receiving relay RR to the receiver TTY. A circuit'is now established from the armature of relay RR over contact 4 of relay LTR, over contact 2 of relay TOR, through resistance R5 and potentiometer P1 to ground. Thus a negative or positive drop may be produced from the sliding contact of the potentiometer P1 to ground, depending upon whether a marking stop pulse or a spacing start pulse is received by the relay RR. l

It should be noted that while timing circuit TG2 was passing through its cycle, the condenser C1 was charged to a negative voltage with reference to ground over contact 5 of relay SGR1. Assuming this voltage to be 130 volts negative, the condenser C1 Would be charged accordingly. This condition exists at the instant relay SGR1 operates to remove negative battery from the condenser C1 and the grid of tube VT1, to start the cycle of timing circuit TG1. With condenser C1 charged to this voltage, rheostat R1 is set so that the condenser C1Will discharge through itin 31 milliseconds, and thus bring the plate current of tube VTi up to full operating value at the end of that period.

As previously stated potentiometer P1 is connected to the armature of receiving relay RR upon the operation of relay LTR to close its contact 4. Let us assume that the IR drop from the sliding contact of potentiometer P1 to ground is l0 volts, positive or negative, depending upon the position of the armature of relay RR. If this drop is negative (as Yit is when a stop pulse is received) the total voltage to ground of condenser C1 is 140` volts negative. When a start pulse begins, the drop through the potentiometer is positive,l and the total drop through which condenser C1 must discharge is reduced to 120 volts negative. The condenser C1 Will therefore require more or less than 31 milliseconds to discharge, depending upon which of these two conditions exists.

Now if the potentiometer is adjusted so that,

with a closed circuit marking pulse being reopen its contact 5 and start the cycle of timingcircuit TG1, the drop through the potentiometery P1 will vbe changed from negative to positive,r and condenser C1 'will be fully discharged immediately. vVacuum vtube VT1 would :therefore become fully Yconductive at the instant the transition was receivedlby the relay RR.

. Thefull plate current now flowing through contact of relay SGR1 to the grid of vacuum' tube VT1 so that its plate currentis instantly reduced to zero, butthe current in relays L'IR and SGRz is Vmaintained for .22`milliseconds by the charging of condenser C5, after which relay SGRg is operated lto again close its contact 4. YBy opening itscontactSrelay .SGR1 starts the discharge of condenser@ of timing circuit TCz, thus initiatingits 132mil1isecondcycle. While the'reoperation of relay SGRz to close its contact 4 closes the connection to receiver TTYover contact'll of relay TOR at this point, saidcircuit isheld open at contact lofA relay SGR1. Hence the open circuit start condition is maintained in the circuit to receiver TTY until, after relay LTR has-operatedito close its contact 5, the vfirst character determining pulse is transmitted over said contact to the receiver.

From the foregoing it Will readily. `be seen that the combined operation of the receiving relay RR, potentiometer P1, and the stop pulse timing circuit TCnoperate to correct for time differentials between received and locally generated stop-start pulsesiof plus orminus a predetermined amount.

To summarize, it will be evident from the foregoingthat a stop pulse is locally supplied to the receiver `during the timecycle of timing circuit TCi.. f. Also that at thelend of said cycle a start `pulseislocally supplied to the receiver andthe time cycle 'of .timing circuit TCz is initiated. Further it will be clear that during said cycle of timing circuit TC'z characterdetermining pulsesare received from the loop Ly and transmitted overcontact 5 of relay LTR to the receiver; .It willlikewise be seen thatvat the end ofthe cyclefof timing circuit TCz the` cycle of timing circuit'TCi is again startedy and theforegoing process is then repeated. Obviously the repetition of these operations will cause locally generated stop-start pulses to be continually supplied tothe-receiver TTY as long as relay TOR is operated.

" 'General description lo f apparatus of Fig. 2

The circuit arrangement ofY Fig. 2 includes apparatus in all respects similar to that-of Fig. 1, except'that a regenerative repeater arrangement is substituted for the timing circuit TC2, and certain minor changes are made in the wiring, these changes being necessitated by the use of the regenerative repeater. The use of the regenerative repeater has the advantage that it regenerates the signal pulsesbefore` they are transmitted tothe receverTTY.

The regenerative lrepeater is shown at RGR and includes, inaddition to a receiving magnet RRM, three cams; aso-called armature cam AC, aflockin'g cam LC, and arelease ,holdingcam RHC. The receiving magnet is 'of the typeknown as a holding magnet, in which themagnetic force is only suicient to hold the armature after it is presented to the pole faces by the raised portions or teeth on the surface of the cam AC.

'I'he armature is operatively connected to a flexible sending contact reed SCR, which may be caused to travel between its marking and spacing contacts. The reedV SCR may be Atemporarily locked against either contact by means of a detent on a lock arm LA. This is controlled by the raised portions or teeth on the surface of the locking cam LC. The connection between the armature .AR and the sending contact reed SCR is suiiiciently flexible so that when the armature is released by the magnet RRM, and therefore drops to the surface of the cam AC, the sending contact reed may. still be held locked in its marking position. Consequently it will be snapped suddenly to its spacing contact when it is released by a tooth on the locking cam LC' momentarily operating the lock arm LA. As soon as the lock arm drops down on the other side of the cam tooth of locking cam LC, its detent locks the sending contact reed against its spacing contact.

Vice versa, when the armature is lifted into the eld of. the magnet RRM by a tooth on the armature cam AM and is held up by a marking pulse, the reed vSCR remains locked against its spacing contact until it is permitted to snap back to its marking by the next tooth on cam LC operating the locking arm LA,

The teeth upon the locking cam are so off-set with respecttothose on the armature cam that they permit the sending contact reed to be snapped over to its opposite contact about the middle of the pulse controlling the lreceiving magnet RRM. It will be noted that the sending contact reed SCR remains-in either of its positions for the full interval of a pulse. Consequent-- i ly the impulses repeated by it are renewed waves with square tops and are not affected by the distortion which modies the shape of the Waves received by the magnet RRM.

The relay holding cam RHC controls a contact y HC which controls the current of relays SGRi and LTR in a manner similar to the control exercised in Fig. l by vacuum tube VTz. However the relays are so-poled that their armatures 0perate to their number 5 contacts, instead of their number 4, when their operating ywindings o receiye current. The contact HC is controlled in such a way that it is opened only when the cam assembly is near the stop position. The lever HL operating the contact is modified with respect to the corresponding lever ordinarily employed in a; regenerative repeater (see dottedl lines), by elongating the cam rider so that contact HC will be opened just before the receiving armature AR is presented to the magnet RRM for the stop pulse. As contact HC controls relays SGR1 and LTR, and the former transmits the stoppulse tothe receivingmagnet RRM,"the openingof contact HC' must precede the presentation of armature AR to the magnet for the stop pulse. `It will be noted that the battery connectionto thewindings of relays SGR1 and LTR are reversed With respect to the rcorresponding 'relays of Fig. l. Therefore it is only when the circuit cf the .biasing vwindings is opened that the armatures of these relays rest on their number lcontacts, and it is the closure ofV contact'I-IC that moves them to their number 5 contacts.

The receiving' magnet RRM in addition to performing the functions above described, also-serves in response to astart pulse to tripk a'latch (not shown) which starts the rotation of the shaft upon which cams AC, LC and RHC are mounted. Operation of the trip latch permits the cam assembly to rotate under power received through a friction clutch. Upon a stop pulse being received the magnet RRM causes the trip latch to lock the shaft until released by another start pulse. f

When the receivingmagnet RRM receives a start impulse it releases its armature AM, and the trip latch (not shown) controlled by it releases the cam shaft. The release of the armature AR does not at once shift the sending contact reed SCR from marking to spacing, as the reed is still locked by the detent of lock arm LA. As the middle of the start pulse is approached, however, the start tooth on cam LC operates the arm LA and the reed SCR snaps to spacing. As soon as described is sufficient to insure the operation of 5. With tube VTi disabled, and with contact 4 of relay LTR opened, negative battery flows through resistance R4 to cause relay SGRZ to restore `its arma-ture to its contact 4.

Just before theA cam shaft of the repeater IRGfR completes vits 'rotation cam RHC opens contact HC. This occurs just before the stop pulse is received.. Relay .SGR1 now shifts its armature the tooth on cam LC passes the rider of lock arm v LA, the detent carried by the lock. arm is moved so that the reed is locked against its spacing contact.

If the rst character forming pulse is also a spacing pulse, tooth 1 of cam AC presentsthe armature AM to the magnet RRM just before the middle of the pulse. A moment later the tooth of cam AC releases the armature, but since the magnet is not energized the larmature falls back against the surface of the cam AC. When shortly afterward the number 2 tooth of cam LC releases the sending contact reed SCR, the reed remains against the spacing contact, and an instant later is locked there by the detent of the locking arm LA.

If the second character forming contact happens to be marking, when the number 2- tooth of cam AC presents armature AM to the magnet RRM the armature is held up. The reed SCR remains locked against its spacing contact until the number 2 tooth of locking cam LC releases it. It then snaps 4over to the marking contact and a moment later is locked there by the detent of locking arm LA. The operations for other pulses, including the stop pulse, are similar to the operations just described. The sending code reed SCR, of course, repeats the pulses to the receiver TTY.

(relay TOR not operated) In general the operation is similar to' that of Fig. 1. When relayTOR is not operated the start pulse, character forming pulses, and stop pulse are transmitted to receiver magnet RRM over contact 3 of relay TOR. The start pulse causes magnet RRM to release the. cani shaft, which, as it rotates, repeats the pulses into the receiver TTY in the manner already described. In response to the open circuit start pulse, receiving relay RR connects positive battery over contact l of relay TOR to winding o of relay SGRz. Relay SGRz shifts its armature to contact 5, but without producing any result, because the closing of contact HC by cam RHC of the regenerative repeater energizes the operating winding o of relays ySGfRi and LTR. It will be noted that in the idle condition of the system these windings received no current. n

Relays 'SGRr and LTR now shift their armatures to their number 5 contacts, the latter about 2 milliseconds after the former (due to the action of condenser C3) where they remain until just before the cam shaft of the repeater has completed its rotation, when the contact HL is opened. Thisv takes place just before the stop pulse is relayed to receiver TTY. The delay. of 2 milliseconds above from contact 5 to contact. Il, and 2 milliseconds later relay LTR shifts its contact. When the armature of relay SGR1 opens its contact 5 condenser C1 begins to discharge. The condenser is fully discharged and the tube VT1 develops full plate current under normal conditions in about 31 milliseconds. When relay LTR closesl its contact 4 negative stop current is supplied to potentiometer P1, to be followed approximatelyr 31 y milliseconds later by positive start current from the yarmature of relay RR. This stop-start transition, acting through potentiometer P1, synchronizes the time cycle of timing circuit TC1 in the same manner as described in connection with the circuit of Fig. 1. y

At the end of its cycle vacuum tube VTi fully energizes winding b of relay SGR2, but the arma ture of said relay may be held against itscontact 4 by the negative stop current through its winding o from the armature of relayl RR1. Normally the start pulse is received at once however, and the resulting positive current passing through Winding lo of relay -SGRZ from the armature of relay RR causes relay SGR2 to again open its contact 4. The operations above described are now repeated for the next character.

Reception of characters by circuit of Fig. 2 after relay TOR operates Let us assume that some time during the recep-r tion of the second character relay TOR operates. At this time the armatures of relays SGR1' and LTR are on their number 5 contacts, and the armature of relay SGRz is on its Contact il. The operation of relay TOR open's its contact l and thereby removes the winding o vof relay SGRz from any further control by impulses received fromthe loop L. Atcontacti it opens the direct pulse connection to the receiving magnet RRM of the repeater. Thenceforward character forming pulses must be transmitted to said magnet over the alternative path closed at contact 5 of relay LTR. At contact 4 of relay TOR a new stop-start pulse circuit is connected to the receiv` v:ing magnet RRM, this new circuit being controlled by the armatures of relays SGRi and SGRa u Just before the cam shaft of repeater RGR completes its revolution cam RHC opens the circuit of the'operating windings of relays SGR1 and` LTR. Relay SGR1 at contact 4' now completes ay tiomter Pi the synchronizing circuit previouslyl described. i y f After the usual delay ofv "'Affter 31-milliseconds more ori-less, depending `pulse condition in the path over-contact 4-of relay TGR continues until character'determining -pulses are transmitted -to receiving magnet RRM over contact y5 of relay LTR,

As the cam shaft ofthe repeater -RGR completes its revolution the circuit for the operating windings of relaySGRl and LTR are again closed; Relay SGRi' opens its contact '5 yand thereby starts the cycle timing circuitTCi to again generate locally a stop pulse followed by a 'start pulse.

"The foregoing operations are repeated -for subl sequent :characters so long as relay-TOR remains operated.

While this invention has been disclosed in certain specic arrangements which are-deemed desirable, it will be obvious that the'fgeneral principles herein set forth may be embodied in many other organizations, widely diierent from rthose illustrated, Without departing from the spirit of this invention as defined in the-appended claims.

What is claimed is:

1. In a teletypewriter system, means to transmit toa receiving station in uniform timed sequence a succession of code combinations including character determining pulses andsynchronizingpulses, a receiving device at a receiving station to record received code combinations, pulse generating means at said receiving station to locally generate synchronizing pulses in substantially the same sequence and time of duration as those normally received,and means to supply, said locally generated pulses to said' receiving device.

2. In a teletypewriter system, -meansto transmit to a receiving stationin uniform timed sequence a succession of code combinations including character determining pulses and synchronizing pulses, a receiving device at a receiving station to record received code combinations, pulse generating means at said receiving station to 'locally generate synchronizing pulses in substantially thesame sequence and time ofl duration as .those normally received,means operating after the initial transmission of signals to prevent synchronizing pulses receivedirom a distant' sending station from being transmitted'tosaid receiving device but permitting character deterto said receiving device.

"4.-In afteletypewriter system,v means to transmit to a receiving stationv in uniform timed sequence a succession -of code combinations including character determining pulses and'synchrof nizing pulses, `av receiving device Aat a receiving station to record received code combinations, pulse'generating means at said receiving station to locally generate-synchronizing pulsesin substantially the same sequence and time of duration as those normally received, means operating after the initial transmission of signals to prevent synchronizing pulses received from a distant sending station from being transmitted to said receiving device but permitting character determining'pulses to be transmitted thereto, means to utilize said synchronizing pulses received from a distant station to control the operation of said pulse' generating means so that the pulses generated thereby will -be synchronized with said received synchronizing pulses, and means to supply the locallyv generated pulses thus synchronized to said receiving device.

5. In a'teletypewriter system, means to transmit to a receiving station in uniform timed sequence a succession -of code ycombinations each including a start pulse, a set of -Baudot character determining pulses and a stop pulse, the start pulse of a succeeding code combination immediately following the stop pulse of the preceding combination, a receiving device at a lreceiving station to record received code .combina-tions, stop-start pulse generating means at said receiving station tolocally generatestop-start pulses in substantially thesame sequence and timeV of duration as those normally received,land means -to supply said locally'generated stop-start pulses to said receiving device.

6. In a teletypewriter system, means to transmit to a receiving station in uniform time sequence a'succession of code combinations each including a start pulse, a set of Baudot character determining 1 pulses and a stop pulse, the start pulse of a succeeding code' combination immediately following the stop pulse ofthe preceding combination, avreceiving device ata receiving station to record received code combinations, stop-start' pulse generating means-at said receiving station to locally'generate stop-start pulses in substantially the same sequence and time of duration as those normally received, means operating after the initial transmission of signals to preventV stop-start pulses received from adistant mining pulses to be transmitted thereto,and

means to supply said locally said receiving device.

`3.1In' a teletypewriter system, means to transmitto a receivingfstation in'u'niform timed sequence a succession of code combinations includin g character determining pulses and synchronizing pulses, a receiving device ata receiving station to record received-code combinations, pulse generating means at said receiving station to locally generate synchronizingI pulses in substantiallythe same sequence and time of duration as'tho'se normally received', means responding. to synchronizing pulses received from' a distant generated pulsesto sending staticnfrom being transmitted to said receiving device but permittingBaudot character determining pulses to be transmitted thereto, and meansy to supply-said locally generated 'pulses to said receiving device.

7. In a teletypewriter system', means to transmit to a receiving station in uniform timed sequence a succession of code combi-nations each including a start pulse, a set of YBaudet character determining pulses and a stop pulse, the start pulse of asucceeding-code combination immediately following thestop pulse of the preceding combination, a receiving device at a receiving station to record received code combinations' stop-start pulseagenerating means'at-said receiving station to locallyrgenerate stop-start pulses in substantially the saine"sequenceand' time of duration as those normally received, means re` sponding to stop-start pulses received from a distant sending station to control the operation of said stop-start pulse generating means so that the stop-start pulses generated thereby will be synchronized with said received stop-start pulses,

and means to supply the locally generated pulses to said receiving device.

8. In a teletypewriter system, means to transmit to a receiving station in uniform timed sequence a succession of code combinations each including a start pulse, a set of Baudot character determining pulses .and a stop pulse, the start pulse of a succeeding code combination immediately following the stop pulse of the preceding combination, a receiving device at a receiving station to record received code combinations, stop-start pulse generating means at said receiving station to locally generate stop-start pulses in substantially the same sequence and time of duration as those normally received, means operating after the initial transmission of signals to prevent stop-start pulses received from .a distant sending station from being transmitted to said receiving device but permitting Baudot character determining pulses to be transmitted thereto, means to utilize said stop-start pulses received from a distant station to control the operation of said stop-start pulse generating means so that the stop-start pulses generated thereby will be synchronized with said received stop-start pulses,

and means to supply the locally generated stopstart pulses thus synchronized to said receiving device.

9. In a teletypewriter system, means to transmit to a receiving station in uniform timed sequence a succession of code combinations each including a start pulse, a set of Baudot character determining pulses and a stop pulse, the start pulse of a succeeding code combination immediately following the stop pulse of the preceding combination, a receiving device at a receiving sta tion to record received code combinations, stopstart pulse generating means at said receiving station to locally generate stop-start pulses in substantially the same sequence and time of duration as those normally received, said stop-start pulse generating means including two timing devices, the first one being started upon the reception of the start pulse of the first code combination and having a time cycle substantially equal to the time required to receive a start pulse and a set of Baudot character determining pulses'the second timing device being started upon the completion of the cycle of the first and having a time cycle substantially equal to the time duration of a stop pulse, means to apply a stop pulse condition to said receiving device during the time cycle of said second timing device, means to apply a start pulse condition to said receiving device after the completion of the cycle of said second timing device, and means operating after the completion of the cycle of said second timing device to start the cycle of said rst timing device anew.

10. In. a teletypewriter system, means to transmit to a receiving station in uniform timed seduence a succession of code combinations each including a start pulse, a set of Baudot character determining pulses and a stop pulse, the start pulse of a succeeding Code combination immediately following the stop pulse of the preceding combination, a receiving device at a receiving station to -record received code combinations, stopvstart pulse generating means at said receiving station to locally generate stop-start pulse in sub.

stantially the same sequen-ce and time duration as those normally received, said stop-start pulse generating means including two timing devices, the iirst one being started upon the reception of the start pulse of the first code combination and having a time cycle substantially equal tol the'time required to receive a start pulse and a set of Baudot y.character determining pulses, the second timing device being started upon the completion of the cycle of the first and having a time cycle substantially equal to the time vduration of a stop pulse, means to apply a stop pulse condition to said receiving device during the time cycle of said second timing device, means to apply a 'start pulse condition to said receiving device after the completion of the cycle of said second timing device, means operating after the completion of the c'ycle of said second timing device to start the cycle of said rst timing device anew, and means operating after the initial transmission of signals to prevent stop-start pulses received from a distant sending station from being transmitted to said receiving device.

l1. In a teletypewriter system, means to tran-smit to a receiving station in uniform timed sequence `a succession of code combinations each including a start pulse, a set of Baudot character determining pulses and a stop pulse, the startpulse of 'a succeeding code combination immediately following the stop pulse of the preceding combination, a receiving device at a receiving station to record received code combinations, stop-start pulse generating means at said receiving station to locally generate stop-start pulses in substantially' the same sequence and time of duration as those normally received, said stopstartpulse generating means including two timing devices, the iirst one being started upon the reception of the start pulse of the first code combination and having a time cycle substantially edual to the time required to receive a start pulse and a set of Baudot character determining pulses, the second timing device being started upon the completion of' the'cycle of therstand having a time cycle substantially equal to the time duration of a stop pulse, means to apply a stop pulse condition to said receiving device during the time cycle of said second timing device, means to apply a start pulse condition to said receiving device after the completion of the cycle of said second timing device, means operatingr after the completionv of -the cycle of said second timing device to start the cycle of said first timing device anew, and means responding to stop-start pulses received from a distant sending station to synchronize the operation of vsaid stop-Start pulse generating means .so that the time cycle of said second timing device will be terminated and the time vcycle oi said first timing device will be started anew atv the instant a stop-start transition occurs between successive code combinations received fron-ia distant sending station.

12. In a'teletypewriter system, means to transmit to a receiving station inuniform timed sequence a succession of code combinations e'ach including a start pulse, a set of Baudot character determining pulses and a stop pulse, the start pulse of a succeeding code combination immedi-` stop-start `pulse generating-means. including.; two timing devices theflrst.y one being.` startedupon thereceptionof .the start pulse of the iirstcode. combination Vand having a. .time cycle substantial@ ly,equa1.- .tothe .time required to receive va.. start. pulseand a set of.Baudot.charactendetermining. pulses, the second timing Adevice being-.started uponthe completion. of the` cycle -of I the vfirst and havinga time cycle substantially vequaltov the timecdurationof a stop pulse-means to-.apply a stop :pulse condition .to said rreceiving devicev during-:thettime lcycle of saidsecond timing devicey meansito-.appl-yastart pulse condition to said receiving deviceiafter .-the completion ofthe. cycle of. saidi second f timing-l rdevice, means operating after :the completion of the. cycle oisaid-` second timing- 1,device to `start the. cycle of saidfrst tim` ingdevice-fanew, meansoperating after theinitial transmission. of signals to preventstop-start pulses` received` fromlfa distant` sendingstation from.. being transmitted tosaid receiving-device, ande means: responding.N to. stop-start pulses receivedfrom a distant-sending. station to synchronizethe-:operation of. said .stop-start pulse generating .means .so that the time cycle of said ysec.-

ond .timing-device Wilbbe terminated and the time-.cyc1e of said .iirst timing device will be' started." anew at. the, instant a `.stop-start transitionnoccursbetween 4successive code combinations. receivent froma .distant .sending f station. 1

13..: In. a teletypewriter. system,. means to. transmit. toa receiving -station, in uniform timed sequence. aasuccessionoiV code combinations leach inclluding a `start pulse: a set of. Baudot character determiningpulses anda stop pulse, thestart pulsel of a succeeding t code y combination immediately followingfthe stoppu-lse of the preceding combination, a receivingdevice at a receiving stationcto record received code combinations,

stcp+start pulse generatingmeans at saidk re v ceivingt.stationto...locally= generate stop-start pulses.-.-in substantially y,the samev sequence y and time .ot duration as those. normallyA received,A said stop-start. pulse` generating meansl .including a rst. .and-secondtiming device. eacn including a vacuum..r tuber a condenser..associated with the grid-- orsaid-tube andarrangedtodischarge throught. a resistance 1 at' a =ratetwhich ldetermines the .time required-.tos build up the. platecurrentof the vtubetoiul-l operating value,thereby' completing .the ltime cycle.- of. the timingy device, the timing. cycleot..the.rst timing device being started `upon the reception of: the start pulse ofy the. rst;codecombination.received` and having a Vtime cycle substantially equal-.to the vtimeV re quiredto--recei-ve asi-.art pulse anda-set ofsBaudot. characterv determining pulses-.the timing I cycled or the. second timing `device beingv started uponfthe completion-of thescycle oftherst and having; a-:time-cycle substantially-l equal to 'the time `l.du-ration oa ston-pulsefrneans: to applya stop pulsecondition'ta saidreceivingfdevice duringf the .timef-cycle'fof said` second f timing device,

means` tor apply a start Vpulse vcondition .to said receiving.- devicefaterthe completion-.of the cycle oi-saidfsecond `timing device, and :means operatingafterthe' completion of the: cycle. of said: secondstiming device tostart the cycleA of saidfirst timing Kdevcef -anevw 14ga-Ina teletypevvriter'sys-tem,l means to transmit to.- a receiving.v station inuniform timed 'se-- guance-aV succession of code-combinations each including: a start: pulse;. a :set: oir-Baudetl cl'iaracterv determini-ng' pulses and a# stop-- pulses;- the start pulse of a s'ucceedingccode combination 'immedi-4 ately 4.following vtnestop,` pulseof the precedingV combination, areceiving` device at a receiving station. `to. record received code1combinations, stop-starty pulse generating. means at said receiv-` -v ing station-to locally-generate.v stop-start pulses in substantiallythe same sequence and time of duration as those normally received,` saidstopstart pulse generating means including a nrst and a second timing device each including va Y vacuum tube; a-condenser asscciatedwith'the grid of-said tnesecond timing devicebeingstarted upon thecompletion of the cycle of the first and having mtime cycle substantially'equal to the time duration-ofthe stop pulse, means to apply a ston pulseV condition-1 tosaid receiving device during theftime cycle of said second timing device means-to-apply a start pulse condition to said receivingdevice after the completion of the' cycle y of'said seco-ndftiming device; means operating after..thefcomplctiony ofthe cycle-of said second `'tim-ing deviceto start the cycle` of said rst timing-device anew and` means operatingafterl the initial transmission of signals to prevent` i stopt-start pulses receivedfromt-a distant sending. stationfrombeingtransmitted to said recci-ving. devi-ce.

, 15;In a teletypewriter system, means to tranmit tofa receiving station in uniform timed-- sequence =a succession offcode combinations each including a start pulse, a set of Baudot character determiningfpulses *and* a stop pulse, the start puisant-.a succeeding -cod'efcombination imme-` diatel-y:followingithe stop pulse of the preceding combination, a receiving device at l"a receiving station' to record received vcode `combinations.l

stopfstartfpulse generating` means at said receivingrstation to locallygenerate stop+start pulses in substantially 4the same f sequence and ztime of durationas those Vnormally received, said stop;A start pulse-generating meansincluding a rst: and

a secondtiming device each including avacuum tubefa condenser'iassociated with the grid ofsaid tube andarrangedto' discharge through a resistance'r'at a rate `which 'determines the time required -tofbuild-fup-Jthe plate current of the tube to full` op'erating'value, therebyv completing the time-cycle ofthe-timing device, the timing'v cycle of tliefrst' timing device being started upon the reception-of. the' start pulse of the rst codecombina'tion received` andv having'a `time cycle substantially equalf toV the7 time requiredv to receive a start' puis'eand` .a set of Baudot character deiterm-ining pulses, the timingv cycle of the second, timing; device being'starte'd' upon the completion ofgthe cycle Vof the rstand having a time cycle substantially equal to the -time duration ofv a stop. pulse; means to apply a stop pulse condi tion: to said` receiving device during thel time cycle: of said secondwtiming device, means to ap-y ply a start pulse condition to said receiving deviceafter the. completion' of the cycle of said sec'- ondatiming device;y means operating after the completion !oi the cycle. of said secondy timing# devicefvto. start trie-cycle of `said first timing de-' vice anew, and means responding to stop-start pulses received from a distant 'sending station to synchronize the operation of said stop-start pulse generating means so that the time cycle of said second timing device will be terminated and the time cycle of said rst timing device will be started anew at the instant a stop-start transl tion occurs between successive code combinations received from a distant sending station.

16. In a teletypwriter system, means to transmit to a receiving station in uniform timed sequence a succession of code combinations each including a start pulse, a set of Baudot character determining pulses and a stop pulse, 'the start pulse of a succeeding code combination immediately following the stop pulse of the preceding combination, a receiving device at a receiving station to record received code combinations,stop start pulse generating means at said receiving station to locally generate stop-start pulses in substantially the same sequence and time of duration as those normally received, said stopstart pulses generating means including a rst and a second timing device each including a vacuum tube, a condenser associated with the grid of said tube and arranged to discharge through ,a resistance at a rate which determines the time requiredto build up the `plate current of the tube -to full operating value, thereby completing the time cycle of the timing device, the timing cycle of the first timing device being started 4upon the reception of the start pulse of the first code combination received and having a time cycle subvstantially equal to the time required to receive a start pulse and a set of Baudot character determining pulses, the, timing cycle of the second timing device being started upon the completion of the cycle of the rst and having a time cycle substantially equal tothe time duration of a stop pulse, means to apply a stop pulse condition to said receiving device during the time cycle of said second timing device, means to apply a start pulse condition to said receiving device after the completion of the cycle of said second timing device,

means operating after the completion ofthe cycleof said second timing device to start `the cycle of said first timing device anew, means operating after the'initial transmission of signals to prevent stop-start pulses received from a distant sending station from being transmitted to said receiving device, and means responding to stopstart pulses received from a distant sending station to synchronize the operation of said stopstart pulse generating means so that the'time cycle of said second timing device will be terminated and the time cycle of said first timing device will be started anew at the instant astopstart transition occurs between successive code combinations received from a distant sending station.

17. 1n a teletypewriter system, means to vtransmit to a receiving station in uniform timed sequence a succession of code combinations each including a start pulse, a, set of Baudot character determining pulses and a stop pulse, the start pulse of a succeeding code combination 'immediately following the stop pulse of the preceding combination, a receiving device at a receiving station to record received code combinations, stop-start `pulse generating means at said-rei ceiving station to locally generate stop-start pulses in substantially the same sequenceand time of duration as those normally received` said stop-start pulse generating means including a rst and a second timing device, said second timing device including a vacuum tube, a

'condenser associated with the grid of said tube and arranged to discharge through a. resistance at a rate which determines the time requiredto build up the plate current of the tube to full operating value, thereby completing the timing cycle of said second timing device, said rsttiming cycle of the second timing device being started upon the completion of the cycle of the rst and having a time cycle substantially edual to the time duration of a stop pulse, means to apply a stop pulse condition to the controlling magnet of said first timing device to be relayed to said receiving device during the time cycle of said second timing device, means to apply a start pulse condition to the controlling magnet of said first timing device to be relayed to said receiving device after the completion Yof the cycle of said second timing device, and means operating after the completion of the cycle of said second timing device to start thecycle of said first timing device anew.

18. In a teletypewriter system, means to transmit to a receiving station in uniform timed sequence a succession of code combinations each including a start pulse, a set of Baudot character determining pulses and a stop pulse, the start pulse of a succeeding code combination immediately following the stop pulse of the preceding combinations, a receiving device at a-receiving station to record received code combinations, stop-start pulse generating means at said receiving station to locally generate stop-start pulses in substantially the same sequence and time of duration as those normally received, said stopstart pulse generating means including a rst and a second timing device, said second timing device including a vacuum tube, a condenser associated with the grid of said tube and arranged vto discharge through a resistance atv a rate which determines the time required to build up the plate f current of the tube to full operating value, .thereby completing the timing cycle of said second timing device, said first timing ldevice including a pulse operated controlling magnet, a start-stop cam shaft set into rotation when said controlling magnet receives a startV pulse and ceasing its rotation when said magnet receives a stop pulse, pulse generating cams upon said cam shaft to regenerate pulses received by said magnet and transmit themto said receiving device, the rotating timeA cycle of said cam shaft being substantially equal to the time required to receive a lstart pulse and a set of Baudot character determining pulses, the timing cycle of the second timing de- ',vice being started upon the completion of the `cycle of the flrst and having a time cycle substantially equal to the time duration of the stop pulse, means to apply a stop condition to the controlling magnet of said first timing device to be relayed to said receiving device during .the time cycle of said second timing device, means to ap-. ply a start pulse condition to the controlling magnet of said first timing device to be relayed to .sai dreceiving Ydevicevafter. .the completion :of the .cyelepfvsaid secondv timinggdevice, means oper- A ating-after thecoinpletionof the cycle of said .second timing :device to, start the cycle ofsaid rstgtiming deviceuanevvfand means-operating after the initial transmission of signals Yto preventstop-start pulses received from adistantsending station from-being transmitted .to said receiving device.

19. In a Vteletypevvriter system.- means to transmit to -areceiving stationin uniform timed sequence. a successionof 4code combinations eachl including a start pulse, a setof.. Baudot character determining pulses and a stop pulse, the start pulse of a succeedingcode combination immediately: following l. ,thenstop 1 pulse `of f the r,preceding combination, a yreceiving .device Aata receiving ,Station i to record received code stop-start pulse generating means at said receiving station to locally generate.-stopstart pulses.` in substantially thesamesequence and time of duration as.,- .those` `normally. received, -said stopv.start pulse.r ,generating 7means z ,including a ,f first and-,a second. timing Ydevice,.s: 3.idisecond .timing .,devicelincluding afvacuumtube--a condenser asf ,sociatedwith `the grid .of saidtuberanderranged toldischargethrougha resistanceata rate which determines the timefrequiredtoibuild Aup, the plate v.c urrentof the tubeto fulloperating: value, thereby combinations,

completingthe .timing Vcycle ,ofsaidsecond timing `device, saidrst timing ldevice. including .apulse ...operated A.controlling '..magnetgl a start-gstop cam lshaft set into rotation Whensaidcontrolling magnet receives, a. start ,pulseiand `'ceasing its rotation whensaidmagnet receives a stop,pulse-pulse `regenerating ,cams upon `said ,camshaft to regen- .,erate pulses. received .by said Hmagnet.,and transmit. them vtosaid receiving device, the-rotating u time fcycle. of. .said cam shaft- Ybeing.substantially .equal to the time required to receivea start pulse ,and a. set of .Baudet characterdeterminingY pulses, the. timing cycleofthesecond timing device .being started,..upon.the. completion ,of ,the cycle. ,of the .,iirst .and having a ,time cycle-substantially, equal tothe time .duration .of..a, stop pulse, meansto apply a stop-pulse condition ,to Vthefcontrolling .magnet ,of saidl -rst timing; device `to .bev relayed to said receiving device during the time `cycle lof ,saidsecondtiming device, .means .to apply ai start .pulse condition; to the controlling .magnet -of 'said .first v.timing device to be .relayed vtosaid. receiving rdevice-after the completion .of the cycleof.said

second timingdevice, means operating .atterthe .completion of thecycle of said second ,timing device tov start the cycle of saidrst timing device r i, anew, andmeans responding tasten-start pulses .received from a distant sending-station..to .syn-

chronizefthe operation of `said stopfstart pulse generatingv means so that the -time .cycle ,of .Y said second timing .device .will be terminated yandthe timecycleof vsaid rst timingdevice willbe startedanew at lthe instant,V a stopvstart'; transition occurs between successive vcode combinations -re- ,ceived'froma Adistant sending station.. y

,.ZOLIn-.a teletypewriter system, means to transmitto a .receiving station in uniform timedse- .quencea` successioncf code combinationsieach in: cluding a start pulse, 1a set of Baudot character determining .pulses anda stop pulse, the start Vpulseofa succeeding code combination immedi- ,atelyfollowing' the stop: pulse of the preceding combination, va, receiving deviceat a receiving station to record received code combinations, stopstart pulse vgenerating means `at, said receiving station .to locally.,generateA stopfstart, pulses vin chronize the. operation :ansias -With the grid of said tubeand arranged to .dis-

charge through a resistance at a rate which. determines the time requiredz to build up. .the plate current of the tube to full operating value, thereby completingthe timing cycle of y.said second timing device, said rsttimingdevice including a pulse operated controllingmagnet, a start-.stop

.cam shaft set into rotation when said controlling magnet receives astart pulse and ceasing its rotation ...when saidmagnet receives a stop pulse,

pulse. regenerating cams l.upon said cam shaft'to regenerate pulsesV received; by lsaid magnetrv and transmit them to said receiving device, vthe rotating time` cycle of said cam shaft being substantially equal to the time required to receive a start pulse and aset of Baudot character determining pulses, the timing cycle of the second timingdevice being vstarted upon the. completion. of the cycle of theiirst and having a time cycle. substantially equal to the time duration of a stop pulse, means 4to apply a stop pulse condition rto thecontrolling magnet of said iirst timing device .to be relayed to said receiving device during the .time cycle ofsaid second timing device, means to apply a start pulse condition to the controlling magnet of said rst timing device to be relayed to said receiving device after the completion ofthe cycle of said second timing device, means yoperating after the completion of the cycle of said second timing device to start the cycle of` saidrst timing device anew, means operating after. the initial transmission ofA signals to prevent stopstart pulses received from a distant sending station .from being trans itted to said receiving device, and means responding to stop-start pulses received from a distant -sending station-.to synof said stop-start vpulse generating means so that the time cycle of said secondtimingfdevice will be terminated and the time cycle of said first timing device will be startedanew at the instant a stop-start transition occurs between successive code combinations received from a distant sending. station. 21. In a telegraph system, a start-stop regenerative repeater operable in cyclesl initiated 4by i start impulses, means responsive to'start impulses of received signals forstartingsaid repeater, an incoming channel of transmission for supplying start impulses accompanied by groupsofcode impulses tosaid means of said repeater, an outgoing channel oftransmission to carry regenerated start and code impulses from said repeater, and means for locally lgenerating and limpressing .on said means start impulses in substantial synchronism with the. corresponding impulses of received signals.

22. In a telegraph system, a start-stop regenerative repeater operable-,in cycles initiated by start impulses, vmeans responsive to start Iimpulses of received signals for starting said repeater, an incoming channel of transmission for supplying start impulses accompanied by groups of,l code impulsesto said` means of said repeater,

an voutgoing channel lof transmission to carry reerative repeater operable in cycles initiated by start impulses, means responsive to start impulses of received signalsfor starting said repeater, an incoming channel of transmission for supplying start impulses accompanied by groups of code impulses to said means of said repeater, an outgoing channel of transmission to carry regenerated start and code impulses from said repeater, means local to said repeater for initiating cycles of said 'repeater in the absence of received start impulses, and means for disabling said local initiating means a predetermined interval after cessation of signal reception. 24. In a telegraph system, a start-stop regen- 

